The present invention relates to a tint control circuit for color television receivers.
A tint control circuit for color television receivers usually comprises a phase-locked loop including a phase detector for detecting the difference in phase between the received color burst signal and a color subcarrier provided by a voltage-controlled oscillator to control the frequency of the latter in dependence on the phase difference representative DC voltage. For tint control purposes, manual phase shift of the subcarrier is effected by means of a variable phase shifter which is connected between the color burst source and the phase detector and such variable phase shifter comprises a capacitor, an inductor and a variable resistor which is provided on an accessible location. However, the adjustment of the variable resistor tends to produce an amplitude variation as well as the phase variation and as a result the phase detector might fail in detecting the correct phase difference, which results in a loss of control of the phase-locked loop. Furthermore, since the variable phase shifter is directly coupled to the high frequency signal, and since the variable phase shifter circuit lead runs a substantial length in the receiver, unwanted signals may easily be introduced to the phase shifter and cause a disturbance to the operation of the phase-locked loop.